The present invention relates to a device and a method for reducing a voltage dependent capacitive coupling.
BAW filters and/or BAW resonators formed on a semiconductor base material, such as, for example, silicon, are passive electrical RF devices usually operated in the gigahertz range. BAW resonators exemplarily comprise a bottom electrode and a top electrode separated by a piezoelectric layer and, when applying the resonant frequency, the result will be standing acoustic waves in the BAW resonator. Depending on the material and a layer thickness of the piezoelectric layer, the result will be resonance in the high-frequency band (usually in the gigahertz range). Due to the high frequency, a series of capacitive couplings which are usually undesired and are to be avoided may occur. Examples of this are capacitive couplings between individual conductive tracks or capacitive couplings relative to an electrode of the BAW filter or even via an electrically conductive substrate material.
Capacitive couplings between pads or conductive tracks can, for example, be minimized by a suitable design of pads and conductive tracks. Another way is using a high-resistance semiconductor material (such as, for example, lightly doped semiconductor material) as the substrate material so that capacitive coupling between metal layers via the substrate material can be avoided due to the high electrical resistances of the substrate. A disadvantage resulting from using a lightly doped semiconductor material is, for example, a voltage-dependent substrate capacitance C(U) occurring between metallic patterns in the BAW filter and the substrate. The voltage-dependent substrate capacitance C(U) is generated by the surface effect at metal-oxide semiconductor (MOS) interfaces or boundary surfaces, as is known from MOS transistors.